For example, U.S. Pat. No. 7,043,118 discloses a laser apparatus in which a projecting section of a laser oscillator emits a laser light flux and an optical member such as a lens aligns and guides the emitted laser light flux to a light-receiving member such as an optical fiber. It is known that an output of the laser apparatus of this kind results in Gaussian distribution for a misalignment of the laser light flux.
In the U.S. Pat. No. 7,043,118, the laser light flux is positioned on the optical fiber by the method that is called wobbling. According to the method, an optical member is oscillated minutely at a certain cycle and at certain amplitude, and a change of intensity of a laser light flux in optical fiber is measured. Thereby, a direction and an amount of movement of the optical member to maximize an intensity of the received laser light flux are calculated.
There is also known a control method called mountain-climbing control. According to the method, an optical member is moved by a prescribed amount in the laser apparatus of this kind, then, laser output is checked whether it increases or not. The optical member is moved repeatedly by a prescribed amount in the direction that output of the laser increases until the moment when the intensity of the received laser light flux starts decreasing.
In the aligning control of the laser apparatus described above, the laser output becomes a significant value which is not zero when the alignment is operated in a range of a diameter of, for example, about 1 μm. While, positioning resolution (minimum movement amount) of the optical member is about 100 nm, for example, with an actuator of a friction drive type employing a piezoelectric element.
In a conventional laser apparatus, therefore, it is difficult to position an optical member accurately at the location where the intensity of the received laser light flux becomes the maximum as shown in FIG. 7, for example. It causes aligning errors that a power of an actual outputted laser light flux becomes smaller than the maximum value, which has been a problem.
A laser apparatus used for optical communication is requested to keep a laser output to be constant. To comply with this, it is considered that the laser output is fed back to adjust an output of a laser oscillator. However, it cannot be used together with the alignment control based on the same laser output. Therefore, in the laser apparatus in which an output of the laser oscillator is controlled, even when the laser apparatus causes a misalignment due to manufacturing errors and secular changes, or to rise of temperatures in use, the laser apparatus is controlled so as to increase the laser output. Therefore, the energy efficiency of the laser apparatus decreases, which has been a problem.